Re: New Study Claims Mars Dry for 4 Billion Years


Dear Mr. Smith,

First, let me note that the July 22nd issue of Science is available at
its Website, www.sciencemag.org and that the full text of the article
in question is now available there to the general public. (Click on
"see current issue" then on "research articles" then on the Mars
temperature by Shuster et al.)

The rocks are said to have been ejected into space some eleven million
years ago, and that assertion is based upon cosmic-ray exposure
testing. That opens an entirely different can of worms, so let's stick
to the point of contention/confusion we've been haggling over.

You say that the area of space that the rocks spent their time in
(while in space) varies in temperature between 3 K and 6000 K, and that
"on average" the temperature is somewhere between that of Mars and that
of Earth. That's quite a variation -- anything up to 273.15 K being at
or below freezing -- and it isn't clear to me how meaningful that
average is, because it may merely be mathematical and of no actual
bearing upon temperatures the meteorites have been exposed to.

I suppose I'm confused, if that's the case, because the media
description of the article said: (A) that argon decay analysis -- which
is temperature sensitive -- permitted the study authors to determine
that the near-surface temperature of Mars hasn't, within the last four
billion years, been significantly above the current cold temperature (<
0 degrees Celsius); (B) in support of this thesis, quoted one of the
study's authors as saying "However you look at it, these rocks have
been very cold for a very long time".

OK, you say that space, at least within the area of our Solar System
where these rocks are said to have floated around for millions of
years, isn't cold. Then, I don't see how these rocks could have been
"very cold for a very long time". If the study's authors were merely
referring to a period of a few hundred thousand years during which time
they were (you've said) buried in the Earth's polar regions, how would
this be relevant to the argon-decay testing thesis? The idea, I take
it, is that if these rocks have remained cold, very little argon has
been released, and argon levels in the rocks are comparable to what
they were when on Mars. On the other hand, if they were floating
around in space at temperatures above freezing for millions of years,
they haven't been "very cold for a very long time". Could variations
in their temperature during that period skew the argon-decay analysis
in ways that would invalidate the study's conclusion?

Now that I've read your reply, I'd be curious to know why these rocks
fell at the Earth's poles, and what that might imply about their
orbital trajectories in the period immediately before capture by the
Earth.

Mark Adkins
msadkins04@xxxxxxxxx

.

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